An upright vacuum cleaner typically comprises a main body containing dirt and dust separating apparatus, a cleaner head mounted on the main body and having a suction opening, and a motor-driven fan unit for drawing dirt-bearing air through the suction opening. The dirt-bearing air is conveyed to the separating apparatus so that dirt and dust can be separated from the air before the air is expelled to the atmosphere.
The suction opening is directed downwardly to face the floor surface to be cleaned. The separating apparatus can take the form of a filter, a filter bag or, as is known, a cyclonic arrangement. The present invention is not concerned with the nature of the separating apparatus and is therefore applicable to vacuum cleaners utilizing any of the above arrangements or another suitable separating apparatus.
A driven agitator, usually in the form of a brush bar, is supported in the cleaner head so as to protrude to a small extent from the suction opening. The brush bar is activated mainly when the vacuum cleaner is used to clean carpeted surfaces. The brush bar comprises an elongate cylindrical core bearing bristles which extend radially outward from the core. The brush bar may be driven by an air turbine or by an electric motor powered by a power supply derived from the main body of the cleaner. The brush bar may be driven by the motor via a drive belt, or may be driven directly by the motor, so as to rotate within the suction opening. Rotation of the brush bar causes the bristles to sweep along the surface of the carpet to be cleaned to loosen dirt and dust, and pick up debris. The suction of air causes air to flow underneath the sole plate and around the brush bar to help lift the dirt and dust from the surface of the carpet and then carry it from the suction opening through the cleaner head towards the separating apparatus.
Vacuum cleaner manufacturers often provide potential customers with a measure of the “airwatts” developed by their products. This is a measure of the amount of suction provided at the suction opening. The suction of air through the suction opening creates a pressure difference between the air passing through the cleaner head and the external environment, which generates a force acting downwardly on the cleaner head towards the surface to be cleaned. Consequently, a disadvantage of providing a high measure of airwatts at the suction opening is that the sole plate can be sucked onto the surface to be cleaned. This can reduce the amount of air which can enter the suction opening from outside the vacuum cleaner, resulting in a reduction of the efficiency of the cleaner. In addition, the cleaner head can become difficult to manoeuvre across the surface to be cleaned, in particular over carpeted surfaces.
It is known to provide one or more air channels located on the side of the cleaner head to allow additional air to be bled into the vacuum cleaner from the external environment. Providing this additional airflow into the vacuum cleaner can reduce the force with which the cleaner head is pushed on to the surface, and thereby reduce the force required to manoeuvre the cleaner head over the surface to be cleaned. However, a disadvantage of providing this additional air flow into the vacuum cleaner is that the amount of suction developed at the suction opening is reduced, which in turn reduces the pick up performance of the vacuum cleaner.